Phthalocyanine compounds are useful as coatings, printing inks, catalysts or electronic materials. In recent years, they have been extensively studied particularly for their use as electrophotographic photoreceptor materials, optical recording materials and photoelectric conversion materials.
It is known that phthalocyanine compounds generally exhibit many different crystal forms depending on the process of synthesis or the process of treatment and that the difference in crystal form has a great influence on their photoelectric conversion characteristics. For example, known crystal forms of copper phthalocyanine compounds include .alpha.-, .pi.-, .chi.-, .rho.-, .gamma.-, and .delta.-forms as well as a stable .beta.-form. These crystal forms are known capable of interconversion by a mechanical strain, a sulfuric acid treatment, an organic solvent treatment, a heat treatment, and the like as described, e.g., in U.S. Pat. Nos. 2,770,629, 3,160,635, 3,708,292, and 3,357,989. Further, JP-A-50-38543 (the term "JP-A" as used herein means an "unexamined published Japanese patent application") refers to the relationship between a crystal form of copper phthalocyanine and its electrophotographic characteristics. Besides copper phthalocyanine, it has been proposed to use various crystal forms of metal-free phthalocyanine, hydroxygallium phthalocyanine, chloroaluminum phthalocyanine, chloroindium phthalocyanine, etc. in electrophotographic photoreceptors.
A process for synthesizing hydroxygallium phthalocyanine comprising hydrolysis of chlorogallium phthalocyanine is described in Bull. Soc. Chim., No. 1962, pp. 23-26, France (1962) and JP-A-1-221459.
The hydroxygallium phthalocyanine prepared by the process, even with the crystal form being equal, show large variation in performance as a charge generating material of an electrophotographic photoreceptor, particularly sensitivity, charging properties, and a dark decay rate, and it has been difficult to obtain hydroxygallium phthalocyanine with stable characteristics.